Barbarian
 
A Barbarian's primary role in a group of adventurers is as a front-line combatant.
He can also serve as a good scout, thanks to his speed, skill selection, and trap sense.
The Barbarian is an excellent warrior and has a powerful rage. no other can match his sheer physical toughness. While in his berserk fury, he becomes stronger and tougher, better able to defeat his foes and withstand their attacks. These rages leave him winded and he has the energy for only a few each day.

From the Shadow Marches to the Eldeen Reaches, come brave, even reckless warrior. Civilized people call them barbarians or berserkers and suspect them of mayhem, impiety, and atrocities. These "barbarians," however, have proven their mettle and their value to those who would be their allies. To enemies who underestimated them, they have proved their cunning and resourcefulness.

Vandemar's Brief Guide to Being a Barbarian by Vandemar
Barbarian Guide @ TenTonHammer by Ralsu
Bard
 
As a generalist, the Bard can be a powerful ally, able to play any role her party needs. As such, she often makes a great team leader.
Her magic can encourage allies, hold enemies rapt, and even twist the minds of her most dangerous foes to make them fight on her side.
She is an accomplished healer, able to heal all but the most dire wounds.
The Bard is perhaps the ultimate generalist. She makes all the other characters better at what they can do, and she can fill in for any other character when needed. her magic emphasizes charms and enchantments, and while she can only cast a limited number of spells, she can do so without selecting or preparing them in advance.

It is said that music has a special magic, and the bard proves that saying true. Wandering across the land, gathering lore, telling stories, working magic with her music and living on the gratitude of her audience - such is the life of the bard. When chance or opportunity draws them into conflict, bards serve as diplomats, negotiators, messengers, scouts, and spies.

Guide To Building A Bard In DDO by mattllow
Cleric
 
The Cleric serves as the group's primary healer, diviner, and defensive specialist.
She can hold her own in a fight, but generally focuses on healing party members.
The cleric's spell selection can greatly affect her role - she can select from a range of healing spells, damaging spells, and defensive or offensive buffs. Clerics are masters of divine magic, which makes them especially good at healing and destroying undead creatures. An experienced cleric can even bring allies back from the dead. Clerics are also adept in the use of simple weapons and armor, since armor doesn't interfere with devine spells the way it does with arcane magic.
The handiwork of the gods is everywhere: in places of natural beauty, in mighty crusades, in soaring temples, and in the hearts of worshipers. The gods, however, mostly work through their intermediaries: their clerics. A cleric uses the power of her god to make the god's will manifest, which means clerics can be relied on to heal, protect, and avenge.

Guide to the High Level Cleric by binkplayboy
Clerics in a Supportive and Undead Combatant Role by Wynder
Cleric Creation Guide @ TenTonHammer by Zed
The Cleric - Holy Warrior @ GamerGod by Osprey
Cleric/Ranger - The Undead Hunter @ GamerGod by Osprey
Fighter
 
In adventuring parties, the Fighter serves as the front-line melee combatant, charging into the fray while his comrades support him with spells and ranged attacks
As fighters gain experience, they get more opportunities to develop their fighting skills and can master the most difficult ones relatively quickly
The Fighter has the best all-around fighting capabilities of all the classes. Fighters are familiar with all the standard weapons and armors. A given fighter may be especially capable with certain weapons, another might be trained to execute specific fancy maneuvers.

The questing knight, the conquering overlord, the king's champion, the elite foot soldier, the hardened mercenary, and the bandit king-all are fighters. Fighters can be stalwart defenders of those in need, cruel marauders, or gutsy adventurers. Some are among the land's best souls, willing to face death for the greater good. An adventuring fighter might call himself a warrior, a mercenary, a thug, or simply an adventurer.

Fighter Creation Guide @ TenTonHammer by Ralsu
DDO Class Guide: Fighter @ GamerGod by GamerDoug
Fighter Guide @ GameAmp by Redweaver
Paladin
 
The Paladin's chief role in most groups is as a melee combatant, and her spell selection is helpful in battling evil.
She makes a good healer, and her high Charisma opens up leadership opportunities.
The Paladin draws on divine power to heal herself and her allies, wards off harm, protects her from disease, and guards heart against fear. A novice can confront evil, and experienced paladins can smite evil foes, turn away undead and cast from a selection of divine spells.

The compassion to pursue good, the will to uphold law, and the power to defeat evil - these are the three weapons of the paladin. Few have the purity and devotion that it takes to walk the paladin's path, but those few are rewarded with the power to protect, to heal, and to smite. In a land of scheming nobles, unholdy priests, inscrutable dragons, backstabbing guilds, and infernal fiends, the paladin is the final hope that cannot be extinguished.

So You Want to Be a Paladin? by Myan
Paladin Creation Guide @ TenTonHammer by Ralsu
Ranger
 
The Ranger's best role is that of a scout and ranged combatant.
Without the heavy armor of the fighter or staying power of the barbarian, the ranger should focus on opportunistic and ranged attacks.
He can also assist groups with healing and as a melee combatant when needed.
A Ranger can use a variety of weapons and is quite capable in combat. He stands out in the use of ranged combat, raining down a volley of accurate missiles with hi bow or crossbow. his skills also make him adept at finding his prey and avoiding detection. Finally, an experience ranger has such a tie to nature that he can actually draw upon natural power to cast a selection of divine spells.

The wilds are home to the fierce and cunning creatures, such as bloodthirsty worgs and malicious spiders. But more cunning and powerful than these monsters is the ranger, a skilled hunter and stalker. He knows both the hidden hearts of the woodlands and the darkest caves of the underworld, and no strength or weakness of his prey escapes his notice.

Teegan's Ranger Guide by Teegan
The Guide to the Ultimate Archery Ranger @ DDO Forums by starfire_one
Ranger Creation Guide @ TenTonHammer by Zed
Rogue
 
Rogues are highly skilled, and they can concentrate on developing several categories of skills that make them extremely useful additions to a party.
While not capable of prolonged melee combat, a rogue knows how to hit where it hurts, and she can dish out alot of damage with deadly sneak attacks or sometimes ranged attacks.
The rogue's stealth and trap-finding ability make her an amazing scout.
Rogues have a sixth sense when it comes to avoiding danger. Experienced rogues develop near-mystical powers as they master the arts of stealth, eveasion, and sneak attacks. in addition, while not capable of casting spells on their own, rogues can "fake it" well enough to cast spells from scrolls, activate wands, and use most magic items.

Rogues have little in common with one another. Some are stealthy thieves. Others are silver-tongued tricksters. Still others are scouts, infiltrators, spies, diplomats, or thugs. What they do share is versatility, adaptability, and resourcefulness. In general, rogues are skilled at getting what others don't want them to get: entrance into a locked treasure vault, safe passage past a deadly trap, secret battle plans, or a guard's trust.

The Rogue's Rogue - Detect, Disable and Pick by Wynder
Fighter/Rogue - A Beginner's Guide to being a Consistent DPS Monkey by Encaen
Rogue Creation Guide @ TenTonHammer by Ralsu
DDO Class Guide: Rogue @ GamerGod by Flendon
Sorcerer
 
Sorcerers can learn fewer spells than wizards, however, they can cast more spells in a given battle and don't need to prepare their spells ahead of time.
Since sorcerers gain their powers without years of study, they have more time to learn fighting skills and become proficient in a wider array of weapons.
A sorcerer often has a powerful presence that gives him a way with people, and he may serve as the "face" for an adventuring party, negotiating, bargaining, and speaking for others.
A sorcerer defines his role based on his spell selection. A sorcerer who focuses on damage-dealing spells becomes a center of the party's offensive power. Another may rely on more subtle magic such as charms, enchantments, or hold spells. The sorcerer can also act as a healer to warforged, the living constructs that survived the Last War.

Sorcerers create magic the way a poet creates poems, with inborn talent honed by practice. They have no books, no mentors, no theories - just raw power that thye direct at will. Some sorcerers claim that the blood of dragons course through their veins. It is common knowledge that certain powerful dragons can take humanoid form and even have humanoid lovers, and it's difficult to prove that a given sorcerer does not have a dragon ancestor. Sorcerers often have very good looks, usually with a touch of the exotic, that hints at an unusual heritage.

Sorcerer - Warforged Doctor and Diplomat by Oghma
Sorcerer Creation Guide @ TenTonHammer by Shayalyn
So you want to be Dragonblooded? @ DnD Vault by Fallen_Crow
Wizard
 
Wizards are among the most offensively minded spellcasters, with a broad range of options available for neutralizing enemies.
The wizard can also act as a healer to warforged, the living constructs that survived the Last War.
The Wizard's strength is her spells. She learns new spells as she experiments and grows in experience, and she can learn from scrolls she finds. In addition to learning new spells, a wizard can, over time, learn to manipulate her spells so they work better, do more damage or last longer.

A few unintelligible words and fleeting gestures carry more power than the battleaxe, when they are the words and gestures of a wizard. These simple acts make the magic seem easy, but they only hint at the time the wizard must spend poring over her spell book preparing each spell for casting, and the years before spent in the apprenticeship, learning the arts of magic. Wizards depend on intensive study to create their magic. They examine musty old tomes, debate magical theory with their peers, and practice minor magics whenever they can. For a wizard, magic is not a talent but a difficult, rewarding art.